sysdeps/ieee754/dbl-64/slowexp.c

   1 /*
   2  * IBM Accurate Mathematical Library
   3  * written by International Business Machines Corp.
   4  * Copyright (C) 2001, 2011 Free Software Foundation
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU Lesser General Public License as published by
   8  * the Free Software Foundation; either version 2.1 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  18  */
  19 /**************************************************************************/
  20 /*  MODULE_NAME:slowexp.c                                                 */
  21 /*                                                                        */
  22 /*  FUNCTION:slowexp                                                      */
  23 /*                                                                        */
  24 /*  FILES NEEDED:mpa.h                                                    */
  25 /*               mpa.c mpexp.c                                            */
  26 /*                                                                        */
  27 /*Converting from double precision to Multi-precision and calculating     */
  28 /* e^x                                                                    */
  29 /**************************************************************************/
  30 #include "mpa.h"
  31 #include <math_private.h>
  32
  33 #ifndef SECTION
  34 # define SECTION
  35 #endif
  36
  37 void __mpexp(mp_no *x, mp_no *y, int p);
  38
  39 /*Converting from double precision to Multi-precision and calculating  e^x */
  40 double
  41 SECTION
  42 __slowexp(double x) {
  43   double w,z,res,eps=3.0e-26;
  44 #if 0
  45   double y;
  46 #endif
  47   int p;
  48 #if 0
  49   int orig,i;
  50 #endif
  51   mp_no mpx, mpy, mpz,mpw,mpeps,mpcor;
  52
  53   p=6;
  54   __dbl_mp(x,&mpx,p); /* Convert a double precision number  x               */
  55                     /* into a multiple precision number mpx with prec. p. */
  56   __mpexp(&mpx, &mpy, p); /* Multi-Precision exponential function */
  57   __dbl_mp(eps,&mpeps,p);
  58   __mul(&mpeps,&mpy,&mpcor,p);
  59   __add(&mpy,&mpcor,&mpw,p);
  60   __sub(&mpy,&mpcor,&mpz,p);
  61   __mp_dbl(&mpw, &w, p);
  62   __mp_dbl(&mpz, &z, p);
  63   if (w == z) return w;
  64   else  {                   /* if calculating is not exactly   */
  65     p = 32;
  66     __dbl_mp(x,&mpx,p);
  67     __mpexp(&mpx, &mpy, p);
  68     __mp_dbl(&mpy, &res, p);
  69     return res;
  70   }
  71 }